The present invention relates to control system for controlling the operation of one or more vehicle accessories, such as an air conditioner.
Typically, air conditioning compressors are controlled as a function of the sensed temperature in the operator's compartment. When the sensed temperature rises above a preset high limit, the compressor clutch is engaged. When the sensed temperature falls below a low limit, the compressor clutch is disengaged. When the compressor is operating, it reduces the peak power available from the engine for other useful work. This reduces the productivity of the machine. The cycling of the compressor increases the load variance of the engine, thereby reducing the durability life of the engine.
Devices are available which disengage an air conditioning compressor clutch during periods of peak engine load, as sensed by an engine load sensor. One such device is known as the "Passmaster". The "Passmaster" includes a vacuum-operated switch which is attached to the manifold vacuum port on a gasoline engine. A problem associated with the "Passmaster" device is that the compartment temperature may exceed what is desired if the engine load persists above the preset limit of the switch. Another problem of systems with a preset load limit is that such systems do not anticipate changing load cycles and do not operate to minimize variance in engine loading.